Cochlear implants have been developed to assist people who are profoundly deaf or severely hearing impaired, by enabling them to experience hearing sensation representative of the natural hearing sensation. In most of these cases, the individuals have an absence of or destruction of the hair cells in the cochlea which naturally transduce acoustic signals into nerve impulses which are interpreted by the brain as sound. The cochlear implant therefore bypasses the hair cells to directly deliver electrical stimulation to the auditory nerves with this electrical stimulation being representative of the sound.
Cochlear implants have traditionally consisted of two parts, an external speech processor unit and an implanted receiver/stimulator unit. The external speech processor unit has normally been worn or carried on the body of the user and its main purpose has been to detect sound with a microphone and convert the detected sound into a coded signal through an appropriate speech processing strategy.
This coded signal is then sent to the receiver/stimulator unit which is normally implanted in the mastoid bone of the user, via a transcutaneous radio frequency (RF) link. The receiver/stimulator unit includes a circuit that processes this coded signal and outputs a series of stimulation sequences. These sequences are transmitted to appropriate electrodes of an electrode array by respective electrically conducting wires. The array is positioned proximal to the modiolus of the cochlea such that an electrical stimulus output by the electrodes is then applied to the auditory nerve.
As the electrode array is typically surgically implanted within the scala tympani of the cochlea of the recipient, the dimensions of the array and the manner of its insertion must be such so as to avoid damage to the sensitive structures of the cochlea. The dimensions and spiral shape of the cochlea also limit the maximum dimensions, particularly the diameter, and the stiffness of any array used as part of a cochlear implant.
In existing designs, this has limited the number of electrically conducting electrodes that can be incorporated into the array, due in the main to limitations imposed on the number of wires that can extend through the array to the electrodes. Traditional electrode array designs have required one or more conductive wires to be connected to each electrode and as such for an array having, for example 22 electrodes, the minimum number of wires required would be 22. With an increased understanding of the tonotopic nature and behavior of the cochlea, the benefits of providing an increased number of stimulating electrodes within the cochlea to stimulate more discrete sites within the cochlea are now being realized. However, it has been demonstrated that increasing the number of wires in conjunction with an increased number of electrodes unacceptably increases the dimensions and stiffness of the array. Merely reducing the diameter of the wires, in order to keep the overall dimensions unchanged, leads to an unacceptable increase in lead resistance. As a result, this limitation on the number of leads, and hence electrodes, limits the scale and type of electrical stimulations that can be applied to the auditory nerve by the electrode array.
The present invention provides a solution to this problem by allowing an increase in the number of individual electrodes of an electrode array of a cochlear implant in comparison to known arrays while still allowing the array to be readily inserted within a implantee's cochlea.
Further to this, the present invention in combination with new methods of manufacturing electrode arrays as described in the Applicant's co-pending International Patent Application PCT/AU02/00575, provides for significant improvements in the size and design of intra-cochlear electrode arrays than has previously been the case.
Any discussion of documents, acts, materials, devices, articles or the like which has been included In the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.